Such pressure-regulating valves have previously been described. These pressure-regulating valves are particularly needed for the flexible control of a wastegate. It is known that internal combustion engines and turbochargers are not ideal partners. The air flow of the intake air is proportional to an increase in rotational speed. In turbochargers, the relation is entirely different. The air flow here does not increase proportionally, but quadratic with respect to the rotational speed of the turbocharger. To prevent an excessive boost pressure from damaging or destroying the engine at high rotational speeds, a bypass is provided in the turbine housing, which is called a wastegate. The wastegate basically has two end positions: closed and open. In the closed position of the wastegate, the combination of the engine and the turbocharger shows the same behavior as the system without the wastegate. In the interest of protecting the engine from destruction due to an excessive boost pressure at excessive rotational speeds, the wastegate is opened so that the turbocharger can be bypassed and the boost pressure can be lowered. However, since, in particular with gasoline engines, different load conditions require different boost pressures in the characteristic map ranges of the engine in order to ensure optimum combustion, a flexible control of the wastegate is required for various rotational speeds. There is therefore a large operation range of the wastegate between the two end positions mentioned depending on the rotational speed and the engine power. For example, a rotatable flap may be arranged in the wastegate which has to be controlled. Since the installation space in the area of the turbocharger is very hot, pneumatic drives with low temperature sensitivity are in particular used. An actuator of the flap situated in the wastegate is correspondingly configured as a pressure-controlled pressure actuator. A spring arranged in the pressure actuator maintains the flap in the closed position when in a non-energized state.
A pressure-control is required for a variable control of the actuator which, when an excessive boost pressure prevails, opens the flap in the wastegate against the bias force of the spring arranged in the actuator. Such pressure-regulating valves are often configured as electromagnetic pressure-regulating valves having a first port at which the boost pressure of the turbocharger prevails, a second port connected with the pressure-controlled component, for example, the pressure actuator, and a third port often connected to the atmosphere and therefore being at atmospheric pressure. Due to the set of characteristic curves of the internal combustion engine stored in the engine control, a boost pressure is defined for each load condition and range of rotational speed, which, based on the current boost pressure, exists at the second port as a mixed pressure composed of the boost pressure and atmospheric pressure. The level of this mixed pressure at the second port can in particular be influenced by the switching frequency and the modulation of the electromagnetic drive. Switching frequencies of up to 35 Hz are currently common with known pressure-regulating valves. In this case, 35 so-called time slots exist in one second, wherein, depending on the pulse width modulation used, a time slot can be kept open or closed for different lengths of time. With a duty cycle of 100%, a time slot is caused to assume the open position over the entire period so that the current boost pressure of the turbocharger prevails at the second port.
A higher switching frequency of about 300 Hz is desired to allow for an even more precise boost pressure regulation in the interest of optimizing the combustion process and of thereby lowering the fuel consumption and the emission values. Although such a switching frequency could be achieved with the electromagnetic drives used, the known pres sure-regulating valves are, in particular, not designed therefore, these valves having two valve seats, i.e., a first valve seat for interrupting the connection between the third port and the first and second ports, and a second valve seat for interrupting the connection between the boost pressure port and the second and third port. Such a high frequency would have too negative an influence on the oscillation behavior of these known pressure-regulating valves and would compromise the service life of the valve.